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240
ViewsWhy the usage of floating point numbers in switch doesn't worky?
#include <stdio.h>
int main() {
int a = 1.0;
switch (a) {
case 1:
printf ("1");
break;
case 1.0:
printf ("10");
break;
default:
printf ("default");
}
}
3 answers
Answer question0
Because switch depends on exact, plain-data comparison.
Comparisons between floats probably don't work as you expect them to, for example, there's a negative and a positive zero.
See: Is floating point math broken?
For these reasons, you can't "simply" say "a == b" when you mean that, as a human. That's why the C standard simply doesn't allow it as a case in a switch.
Truth is: the fact that you're trying to do that is a good reason for forbidding it! Either you're using floats where you shouldn't (namely, to store a limited set of discrete values), or you haven't really understood how floats work, and using them in a switch statement will lead to unexpected behaviour.
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As for the "Please help me" part of your question, you can probably implement that more-or-less as follows...
rather than
double x=1.,y=2.;
blah; blah; blah;
switch(x){
default: break;
case y: blah; break;
}
try instead something like
double x=1., y=2., xmax=10000., xmin=1.;
int ix=1, iy=2, imax=100;
blah; blah; blah;
ix = ((x-xmin)/(xmax-xmin))*((double)imax);
iy = ((y-xmin)/(xmax-xmin))*((double)imax);
switch(ix){
default: break;
case iy: blah; break;
}
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why can't we use floating point numbers in switch conditional statements?
Because the language definition says so.
Because comparing floating-point numbers for exact equality (which a switch statement implicitly does) is often a bad idea.
Because using floating-point variables as control variables is usually a bad idea. @Steve Summit
No compelling need for this feature.